Auto Increment after delete in MySQL

Question

I have a MySQL table with a primary key field that has AUTO_INCREMENT on. After reading other posts on here I\'ve noticed people with the same problem and with varied answer

Answer 1

Its definitely not recommendable. If you have a large database with multiple tables, you may probably have saved a userid as id in table 2. if you rearrange table 1 then probably the intended userid will not end up being the intended table 2 id.

Answer 2

You can use your mysql client software/script to specify where the primary key should start from after deleting the required records.

Answer 3

MYSQL Query Auto Increment Solution. It works perfect when you have inserted many records during testing phase of software. Now you want to launch your application live to your client and You want to start auto increment from 1.

To avoid any unwanted problems, for safer side First export .sql file.
Then follow the below steps:

• Step 1) First Create the copy of an existing table MySQL Command to create Copy:

  CREATE TABLE new_Table_Name  SELECT * FROM existing_Table_Name;
  

  The exact copy of a table is created with all rows except Constraints.
  It doesn’t copy constraints like Auto Increment and Primary Key into new_Table_name

• Step 2) Delete All rows If Data is not inserted in testing phase and it is not useful. If Data is important then directly go to Step 3.

  DELETE from new_Table_Name;
  

• Step 3) To Add Constraints, Goto Structure of a table

  • 3A) Add primary key constraint from More option (If You Require).
  • 3B) Add Auto Increment constraint from Change option. For this set Defined value as None.

Answer 4

I got a very simple but tricky method.

While deleting a row, you can preserve the IDs into another temporary table. After that, when you will insert new data into the main table then you can search and pick IDs from the temporary table. So use a checking here. If the temporary table has no IDs then calculate maximum ID into the main table and set the new ID as: new_ID = old_max_ID+1.

NB: You can not use auto-increment feature here.

Answer 5

I can think of plenty of scenarios where you might need to do this, particularly during a migration or development process. For instance, I just now had to create a new table by cross-joining two existing tables (as part of a complex set-up process), and then I needed to add a primary key after the event. You can drop the existing primary key column, and then do this.

ALTER TABLE my_table ADD `ID` INT NOT NULL AUTO_INCREMENT FIRST, ADD PRIMARY KEY (`ID`);

For a live system, it is not a good idea, and especially if there are other tables with foreign keys pointing to it.

Answer 6

What you're trying to do sounds dangerous, as that's not the intended use of AUTO_INCREMENT.

If you really want to find the lowest unused key value, don't use AUTO_INCREMENT at all, and manage your keys manually. However, this is NOT a recommended practice.

Take a step back and ask "why you need to recycle key values?" Do unsigned INT (or BIGINT) not provide a large enough key space?

Are you really going to have more than 18,446,744,073,709,551,615 unique records over the course of your application's lifetime?